IIA researchers chart the Sun’s subsurface weather

An international team of solar physicists led by the Indian Institute of Astrophysics (IIA) have traced giant tides of plasma beneath the Sun’s surface at a region called near-surface shear layer (NSSL).

According to a study published in the Astrophysical Journal Letters, the plasma’s currents shift with the Sun’s magnetic heartbeat and could have a far-reaching influence on space weather and earth.

“The near-surface shear layer (NSSL) extending to about 35,000 km in depth is a critical region beneath the Sun’s surface. It is marked by distinct rotational behaviours that vary with depth and changes, over space and time, that relate to active region magnetic fields and the solar cycle,” said the Department of Science and Technology.

It added that astronomers have probed the dynamic inner weather of the Sun — plasma currents just beneath its surface at the NSSL, that pulse in step with its 11-year sunspot cycle.

Apart from IIA, researchers from Stanford University (USA), and the National Solar Observatory (NSO, USA) have traced how these hidden flows shift over time, potentially reshaping our understanding of solar dynamics in general and how the Sun’s interior connects to its outer magnetic behaviour in particular.

Employing helioseismology — an advanced technique that tracks sound waves as they travel through the Sun — the team observed changes in the movement of solar material using more than a decade of data from NASA’s Solar Dynamics Observatory/Helioseismic and Magnetic Imager (SDO/HMI) and the ground-based Global Oscillations Network Group (GONG) of National Solar Observatory (NSO), USA.

Fascinating patterns

The analysis led by Professor S.P. Rajaguru and PhD student Anisha Sen from IIA revealed fascinating patterns — surface plasma flows converge toward active sunspot latitudes, but reverse direction midway through the NSSL, flowing outward to form circulation cells.

“These flows are strongly influenced by the Sun’s rotation and the Coriolis force — the same force responsible for the spin of hurricanes on earth,” the department said.

“To validate our findings, we zoomed in on a massive sunspot region using 3D velocity maps. The localised flow patterns we observed matched the global trends — confirming both surface inflows and deeper outflows,” said lead author Anisha Sen.

These findings give us a better understanding of how the Sun’s magnetic activity is linked to its internal flows and hint that we might still be missing something lurking in deeper layers that truly drives its global dynamics.